RESUBMITTING [PATCH] MTD (kernel 2.4.32): kernel stuck in tight loop occasionally on flash access

["Vijay Sampath" <Vijay.Sampath@aktino.com>]

Resubmitting patch after feedback from Grant Coady and Willy Tarreau.
Changed description and erroneous diff output for dontdiff file.


We are running a Timesys modified version of the 2.4 kernel.
Occasionally we see board lockups on heavy file system and direct MTD
flash accesses. I have traced this down to a bug in the 2.4 MTD code
(chip driver to be specific) and see this problem even in the latest 2.4
kernel (2.4.32). I realize that this problem may not be seen by others
using the stock kernel, but I think it needs to be fixed anyway for
correctness.

The problem is in cfi_cmdset_0001.c, and is present in drivers for other
chips as well. In the function cfi_intelext_sync() function before
calling schedule(), the current process needs to be put to sleep by
calling set_current_state(TASK_UNINTERRUPTIBLE). If it is not put to
sleep, the task remains in the run queue of the kernel and if its
priority is high enough, the kernel will constantly keep scheduling this
process, the state of the chip will never change.

Adding this one line seems to make our lockups go away. There were
questions raised as to why TASK_UNINTERRUPTIBLE. The same driver uses
TASK_UNINTERRUPTIBLE in other similar places while waiting for hardware
to complete erasing etc. I chose the same thing.

I am not subscribed to the mailing list, so please CC me on any replies.

Signed-off-by: Vijay Sampath <vijay.sampath@aktino.com>

---

diff -uprN -X linux-2.4.32/Documentation/dontdiff
linux-2.4.32/drivers/mtd/chips/amd_flash.c
/home/vsampath/my-linux-2.4.32/drivers/mtd/chips/amd_flash.c
--- linux-2.4.32/drivers/mtd/chips/amd_flash.c	2003-06-13
07:51:34.000000000 -0700
+++ /home/vsampath/my-linux-2.4.32/drivers/mtd/chips/amd_flash.c
2005-12-17 14:55:20.000000000 -0800
@@ -1350,6 +1350,7 @@ static void amd_flash_sync(struct mtd_in
 
 		default:
 			/* Not an idle state */
+			set_current_state(TASK_UNINTERRUPTIBLE);
 			add_wait_queue(&chip->wq, &wait);
 			
 			spin_unlock_bh(chip->mutex);
diff -uprN -X linux-2.4.32/Documentation/dontdiff
linux-2.4.32/drivers/mtd/chips/cfi_cmdset_0001.c
/home/vsampath/my-linux-2.4.32/drivers/mtd/chips/cfi_cmdset_0001.c
--- linux-2.4.32/drivers/mtd/chips/cfi_cmdset_0001.c	2004-11-17
03:54:21.000000000 -0800
+++ /home/vsampath/my-linux-2.4.32/drivers/mtd/chips/cfi_cmdset_0001.c
2005-12-17 14:53:42.000000000 -0800
@@ -1687,6 +1687,7 @@ static void cfi_intelext_sync (struct mt
 
 		default:
 			/* Not an idle state */
+			set_current_state(TASK_UNINTERRUPTIBLE);
 			add_wait_queue(&chip->wq, &wait);
 			
 			spin_unlock(chip->mutex);
diff -uprN -X linux-2.4.32/Documentation/dontdiff
linux-2.4.32/drivers/mtd/chips/cfi_cmdset_0002.c
/home/vsampath/my-linux-2.4.32/drivers/mtd/chips/cfi_cmdset_0002.c
--- linux-2.4.32/drivers/mtd/chips/cfi_cmdset_0002.c	2004-11-17
03:54:21.000000000 -0800
+++ /home/vsampath/my-linux-2.4.32/drivers/mtd/chips/cfi_cmdset_0002.c
2005-12-17 14:53:58.000000000 -0800
@@ -1172,6 +1172,7 @@ static void cfi_amdstd_sync (struct mtd_
 
 		default:
 			/* Not an idle state */
+			set_current_state(TASK_UNINTERRUPTIBLE);
 			add_wait_queue(&chip->wq, &wait);
 			
 			cfi_spin_unlock(chip->mutex);
diff -uprN -X linux-2.4.32/Documentation/dontdiff
linux-2.4.32/drivers/mtd/chips/cfi_cmdset_0020.c
/home/vsampath/my-linux-2.4.32/drivers/mtd/chips/cfi_cmdset_0020.c
--- linux-2.4.32/drivers/mtd/chips/cfi_cmdset_0020.c	2004-11-17
03:54:21.000000000 -0800
+++ /home/vsampath/my-linux-2.4.32/drivers/mtd/chips/cfi_cmdset_0020.c
2005-12-17 14:54:09.000000000 -0800
@@ -1036,6 +1036,7 @@ static void cfi_staa_sync (struct mtd_in
 
 		default:
 			/* Not an idle state */
+			set_current_state(TASK_UNINTERRUPTIBLE);
 			add_wait_queue(&chip->wq, &wait);
 			
 			spin_unlock_bh(chip->mutex);